The present invention relates generally to a multiband antenna system for use in a motor vehicle, and more particularly to a one-unit multiband antenna unit suitable for use on a motor vehicle and effective for reception of AM/FM radio signals and further for quasi-microwave communication, for example.
Recently, various types of multiband antenna units adapted for reception of AM/FM radio signals and further transmission and reception of a high frequency band over UHF and suitable for use on motor vehicles have been proposed, such as is disclosed in Japanese Patent provisional Publication No. 61-46601 or 61-227405. These antennae are made such that the antenna unit comprises an elongated inner conductor and an elongated cylindrical outer conductor which are coaxially arranged with each other so as to form a coaxial line. One end of the inner conductor is connected to a quasi-microwave communication antenna element and the other end of the inner conductor and one end of the outer conductor are coupled to a quasi-microwave transceiver mounted on the motor vehicle. A portion of the outer conductor (in the case of the Japanese Patent Provisional Publication No. 61-227405, a conductor tube additionally provided to coaxially encase the outer conductor) is further coupled to an AM/FM receiver which is further coupled to a portion of the vehicle metallic body. However, the motor vehicle has many noise sources such as ignition system, and therefore an important problem encountered in such multiband antennas relates to introduction of noises through the output conductor and so on into the AM/FM receiver, which in turn results in the mutual intervention between the AM/FM reception and the quasi-microwave communication.